The first clear signs that Gordon Brown will reorder Britain's foreign policy emerged last night when one of his closest cabinet allies urged the US to change its priorities and said a country's strength should no longer be measured by its destructive military power.

Douglas Alexander, the trade and development secretary, made his remarks in a speech in America, the first by a cabinet minister abroad since Mr Brown took power a fortnight ago.

The speech represents a call for the US to rethink its foreign policy, and recognise the virtues of so-called "soft power" and acting through international institutions including the United Nations.

In what will be seen as an assertion of the importance of multilateralism in Mr Brown's foreign policy, Mr Alexander said: "In the 20th century a country's might was too often measured in what they could destroy. In the 21st century strength should be measured by what we can build together. And so we must form new alliances, based on common values, ones not just to protect us from the world, but ones which reach out to the world." He described this as "a new alliance of opportunity".

He added: "We need to demonstrate by our deeds, words and our actions that we are internationalist, not isolationist, multilateralist, not unilateralist, active and not passive, and driven by core values, consistently applied, not special interests."

With some neocons in the Bush administration nervous at the direction of Mr Brown's foreign policy, following the appointment of the former UN deputy secretary Lord Malloch-Brown as foreign minister, Mr Alexander went out of his way to underline the special relationship, but challenged the US and its partners "to recognise the importance of a rules based international system".

Mr Alexander's comments came at the end of a day in which President Bush had been forced to defend his policy in Iraq after a report on the effectiveness of the "surge" strategy concluded that the military situation had improved but political and economic targets had not been met.
Mr Brown is expected to fly to Washington shortly, and the groundwork for the trip is being prepared, with officials recognising the relationship between the new prime minister and George Bush will be very different from Mr Blair's.

In addition to Mr Alexander's speech, Simon McDonald, the prime minister's foreign policy adviser, is due to fly to Washington next week to meet Stephen Hadley, the US national security adviser. A Whitehall source said: "It will be more businesslike now, with less emphasis on the meeting of personal visions you had with Bush and Blair."

Another British official stressed that the US-UK "special relationship" was just as important to the new prime minister as it was to Mr Blair. However, the official added: "Bush and Blair went through 9/11 together. So maybe there is a difference." Last month, the outgoing foreign secretary, Margaret Beckett, raised eyebrows in the Bush administration with a speech calling for total nuclear disarmament. It was made in consultation with, and with the approval of, Mr Brown. A British source in Washington said the Brown team was asserting its independence "one policy speech at a time", adding: "It's a smarter way of doing it than have a knockdown argument."

In Mr Alexander's speech, to the Council on Foreign Relations in Washington, he repeatedly argued that although terrorism and extremism sometimes had to be combated by force, victory would not be secured by military means alone.

"Given the interconnected nature of the challenges we face, I would argue that we have to simultaneously be fighting to end poverty, to secure trade justice and to tackle conflict and climate change, as well as working to defeat terrorism and ensure the preservation of our security."

Although Mr Blair also repeatedly highlighted the importance of climate change and global poverty, there is likely to be a greater willingness from the Brown government to speak bluntly to the Americans.

Mr Alexander also urged the US to remain engaged on issues such as climate change and Africa, saying: "There are few global challenge that do not require the active engagement of the US."

His remarks are designed to underline British determination that the US remains committed with other countries to forming a new UN-based agreement on the environment to replace the Kyoto treaty when it expires in 2012.